CAD CAD Specialist Mechanical Design and Manufacturing 2 — Questions and Answers
Question 1: What is the purpose of a 'datum' in GD&T on a mechanical drawing?
- A theoretical exact point, line, or plane used as the reference for measurements and tolerances (Correct answer)
- The maximum allowable dimension of a feature
- A note indicating the material specification
- The location of a machining origin
Correct answer: A theoretical exact point, line, or plane used as the reference for measurements and tolerances
A datum is a theoretically exact reference (point, axis, or plane) from which geometric tolerances and measurements are established.
Question 2: In mechanical CAD, what does the 'first angle' projection method indicate about view arrangement?
- The front view is placed to the right of the right-side view
- The object is between the observer and the projection plane, used predominantly outside the US (Correct answer)
- Views are arranged with top view below the front view
- Dimensions are in metric units only
Correct answer: The object is between the observer and the projection plane, used predominantly outside the US
First angle (ISO) projection places the object between the observer and the plane, resulting in view layouts opposite to the US third-angle standard.
Question 3: What does the term 'feature of size' mean in GD&T?
- Any dimension greater than 1 inch
- A geometric shape defined by a single size dimension, such as a hole diameter or slot width (Correct answer)
- A feature requiring a CNC fixture
- A toleranced note for surface roughness
Correct answer: A geometric shape defined by a single size dimension, such as a hole diameter or slot width
A feature of size is a geometric feature (like a hole, pin, or slot) that can be defined by a single size dimension and has an axis or center plane.
Question 4: Which file format is the universal neutral format for exchanging 3D CAD data between different mechanical CAD software packages?
- .DWG
- .STEP (STP) (Correct answer)
- .IPT
- .SLDPRT
Correct answer: .STEP (STP)
STEP (Standard for the Exchange of Product model data) is the neutral ISO 10303 format used to exchange 3D CAD models across different software.
Question 5: In a mechanical assembly, what is an 'interference fit' (also called a press fit)?
- A fit where the shaft is always smaller than the hole
- A fit where the shaft is larger than the hole, requiring force to assemble (Correct answer)
- A fit designed to allow free rotation between parts
- A fit with exactly zero clearance
Correct answer: A fit where the shaft is larger than the hole, requiring force to assemble
An interference fit has a shaft diameter larger than the hole diameter, requiring press-fitting or shrink fitting to assemble.
Question 6: What is the function of a 'revision block' (or revision table) on a mechanical engineering drawing?
- To list the CAD software version used
- To record a history of changes made to the drawing after initial release (Correct answer)
- To show the drawing scale and sheet size
- To identify who approved the drawing
Correct answer: To record a history of changes made to the drawing after initial release
The revision block tracks all changes made to a drawing after its release, including revision letter, description, date, and approver.
CAD CAD Specialist Mechanical Design and Manufacturing 2
What is the purpose of a 'datum' in GD&T on a mechanical drawing?